Diffusion-optimized tipping paper

ABSTRACT

A method for producing a diffusion-optimized tipping paper for tobacco products, especially filter cigarettes, by plasma perforation of the web of tipping paper for the purpose of maximum carbon monoxide reduction, wherein the diffusivity and the permeability P of the perforated tipping paper are measured in-line and diffusivity is maximized by controlling the perforation parameters, the definable target permeability P soll  being maintained at all times.

The invention relates to a regulating method for the perforation ofmouthpiece lining papers, for achieving maximum reduction of carbonmonoxide, and a mouthpiece lining paper manufactured according to thismethod.

The reduction in the CO concentration during smoking a cigarette takesplace on the one hand by the so-called dilution of the smoke which takeplace by the introduction of air into the interior of the cigarettethrough the end of the tobacco strand, pores in the cigarette paper andthe wrapping paper or additionally by holes which have been establishedby perforating, respectively, and on the other hand by diffusion of thecarbon monoxide through the pores or the holes which have beenestablished by perforating, respectively, from the interior of thecigarette to the outside. Diffusion of the carbon monoxide thus takesplace through the same pores and holes as the introduction of air, butin the opposite direction. Diffusion of the carbon monoxide towards theoutside may also be considered to be a gas exchange, since in thisprocess gases such as oxygen, nitrogen, etc. are diffused into theinterior of the cigarette. The dilution of the smoke by means of theintroduction of air is often also referred to as ventilation, adistinction being made between filter ventilation and tobacco-strandventilation, depending on through which part of the cigarette the airmakes its way into the interior of the cigarette.

The drag resistance of the cigarette is relevant for the extent ofdilution. Said drag resistance determines how high the volumetric flowis of fresh air which is sucked in through the pores and holes of thecigarette when smoking. The ratio of the volumetric flow of fresh airthrough the pores and holes of the individual parts of the cigarette tothe total volumetric flow through the mouth end of the cigarette isreferred to as the degree of ventilation, there also being a distinctionhere between a degree of filter ventilation and a degree oftobacco-strand ventilation.

It is desirable in finished cigarettes that they have uniform dilutionor drag resistance or a uniform degree of ventilation, respectively,since the degree of ventilation can substantially influence and modifythe flavour of the cigarette.

The degree of ventilation is derived depending on the permeability ofthe cigarette paper and of the mouthpiece lining paper. Therefore, it isnecessary for the permeability of both the cigarette paper and of themouthpiece lining paper to be kept constant during manufacturing.

In order to be able to set a constant permeability which is independentof the properties such as porosity (ratio of cavity volume to totalvolume) of the used base paper, the base paper for the mouthpiece liningpaper is provided with an additional, adjustable perforation.

Apart from the tobacco strand and the filter, a common filter cigaretteor even a conventional cigarette tube is composed of the cigarette paperwrapping the tobacco strand, the highly porous filter wrapping paper,and the mouthpiece lining paper. A highly porous filter paper isrequired when offline or pre-perforated mouthpiece lining paper is used.

The mouthpiece lining paper, often also referred to as “tipping paper”or “tipping”, for short, enshrouds the filter and the filter wrappingpaper. This is that part of the filter cigarette which is contacted bythe lips of the person smoking the cigarette while the filter cigaretteis being smoked. Typically, the tipping paper also slightly protrudes inthe longitudinal direction of the filter cigarette into the longitudinalregion of the tobacco strands, there wraps itself around the cigarettepaper and is connected thereto by an adhesive connection. On account ofthis adhesive connection being established, the filter part and thetobacco-strand part are mechanically interconnected in thecigarette-making machine. The tipping paper most often is indeed apaper, but may also be a film or a foil, for example. In the event ofthe tipping paper being configured as a film or a foil, the former maybe composed of cellophane. The mouthpiece lining paper usually has avisually appealing printed design. This printed design often resemblescork.

At the tobacco-strand end the mouthpiece lining paper is usuallyconfigured so as to be partially perforated such that during drawing onthe cigarette, air from the environment makes its way into the filterand there is mixed with the smoke stream coming out of the tobaccostrand, reducing the smoke values.

Typically, the mouthpiece lining paper is perforated after printing inorder to prevent the perforation holes being closed again by theprinting operation.

Since the filter wrapping paper which lies below the mouthpiece liningpaper is implemented so as to be highly porous, the total or residualpermeability of the cigarette in the region of the filter is limited byway of the porosity of the mouthpiece lining paper. The porosity of themouthpiece lining paper may be obtained by way of the hole size or thehole count produced by perforating, respectively.

Thus, if the remaining cigarette parameters (porosity of the cigarettepaper, of the filter wrapping paper, drag resistance of the tobaccostrand and of the filter etc.) as well as a pre-defined target value forthe degree of ventilation or the smoke values of the cigarette,respectively, are known, a nominal value for the permeability of themouthpiece lining paper may be pre-defined. The target values for thedegree of ventilation and of the smoke values are usually pre-defined bythe cigarette manufacturer, so that the nominal value for thepermeability can subsequently be established by the mouthpiece liningpaper manufacturer and be referred to during the production of themouthpiece lining paper.

There are methods in the prior art which serve for regulating thepermeability of the mouthpiece lining paper to the pre-defined nominalvalue by way of perforating.

EP 0056223 A2 shows a method for regulating an electrical perforatinginstallation in which the permeability of the paper web is determined byway of the proportion of an electromagnetic wave passing through andbeing reflected (visible light, for example) which is directed onto theperforated paper web. The deviation of the actual value from the nominalvalue of permeability is used for regulating the spark energy.

DE 3016622 A1 shows a method for regulating an electrical perforatinginstallation in which the permeability of the paper web is measured. Themeasured value thus obtained is used for regulating the hole size or thehole count of the perforation by way of the frequency and the durationof the discharges and/or the web speeds.

DE 2833527 A1 shows a method for regulating an electrical perforatinginstallation in which the permeability of the paper web is measured. Themeasured value thus obtained is used for regulating the hole size of theperforation by way of the frequency of the discharges. This may takeplace in that in the case of a sufficiently high frequency a pluralityof discharges are performed so as to be mutually successive through thesame perforation hole and in that the latter is thus somewhat widenedwith each discharge. It is provided that compressed air for cooling theelectrodes is blown in the direction of the ends of the latter.

DE 2802315 A1 shows a method for controlling an electrical perforatinginstallation in which the porosity of the paper web is measured in atesting device. The measured value thus obtained is used for controllingthe hole size of the perforation by way of the frequency of thedischarges or by switching off individual electrode pairs in order tocontrol the perforation-hole count in this manner.

In the perforating installations and the regulating methods of the priorart the effect of the perforation on the diffusion of carbon monoxidehas not been considered to date. The reason therefor may lie in thatthere has been a predominant opinion to date that the diffusion ofcarbon monoxide is not influenced by the perforation, or that saiddiffusion of carbon monoxide cannot be influenced by way of theperforation, in the event that a constant permeability is to beobtained.

Since the reduction of carbon monoxide constitutes a substantial healthaspect, it has been a concern of the applicant to research the effect ofthe perforation on the diffusion of carbon monoxide and to develop adiffusion-optimized mouthpiece lining paper.

The object underlying the invention is to provide an improved method forperforating the mouthpiece lining paper, wherein the reduction of carbonmonoxide in the smoke is to be maximized at constant permeability of themouthpiece lining paper.

In order to achieve the object it is proposed that perforating themouthpiece lining paper which is available as a continuous paper web orfilm web is performed in a regulated perforating device, whereindiffusivity and permeability of the perforated mouthpiece lining paperare determined inline, that is to say directly on the perforatingmachine, and diffusivity is maximized by regulating the perforationparameters while constantly adhering to the pre-definable permeability.

One possibility consists in measuring the hole size of the holes of themouthpiece lining paper produced by perforating and to control theperforation parameters such that the hole size for maximum diffusion ofthe carbon monoxide is established. The permeability of the mouthpiecelining paper is kept constant in that the perforation-hole count isobtained or controlled, respectively, depending on the hole sizeobtained.

On account of this two-step regulating method it is achieved thatdiffusion of carbon monoxide through the perforation is maximized andpermeability is kept constant.

As will be explained also in theory in the following, the applicant hasdetermined that the diffusion of carbon monoxide is at its maximum whenthe hole diameter of the individual perforation holes is minimal. Since,for technical reasons, the hole diameter cannot be implemented so as tobe arbitrarily small, the method according to the invention consists inregulating the hole diameter to the minimum hole diameter achievabledepending on the application and in adapting the number of perforationholes thereto in order to achieve the required permeability. Incomparison with the prior art it is advantageous that maximum reductionof carbon monoxide is achieved while adhering to the specifications forpermeability. The concentration of the undesirable carbon monoxide isthus reduced as far as possible without influencing the flavour and thedrag resistance of the cigarette.

The regulating method according to the invention is best implementedusing the method of plasma perforation which has been developed by theapplicant. On the one hand, plasma perforation makes extremely smallhole diameters possible in the first place, and on the other hand plasmaperforation allows very specific and fast regulating of the perforationparameters.

The invention is visualized by way of drawings in which:

FIG. 1 shows the theoretical correlation between the hole radius r ofthe perforation and the area A which is available for diffusion,depending on the hole count N at constant permeability P;

FIG. 2 shows the design of an exemplary plasma perforation head in asectional view;

FIG. 3 shows the design of a further exemplary plasma perforation headin a sectional view;

FIG. 4 shows the design of a further exemplary plasma perforation headin a sectional view, having a laser as an energy source;

FIG. 5 shows the schematic design of a first variant of regulation,according to the invention;

FIG. 6 shows the schematic design of a second variant of regulation,according to the invention;

FIG. 7 shows the schematic design of a perforating installationaccording to the invention, with a schematic illustration of regulation.

First, the physical approach in theory will be explained, without theintention of being bound to the theory.

The reduction of carbon monoxide takes place by diluting the smokestream and by diffusion. The reduction of carbon monoxide by dilutingthe smoke stream is determined by the permeability P of the cigarette;consequently, in the case of a pre-defined, constant permeability P,maximizing the CO reduction has to take place by way of maximizingdiffusion.

Prior to showing the solution by way of a mathematical approach, thepossibility for maximizing diffusivity at constant permeability P willbe described by way of the physical correlations. In this documentpermeability is understood as being the permeability of the mouthpiecelining paper on account of a pressure differential. The pressuredifferential is generated by drag on the cigarette. In rough terms,permeability here is a measure of how much fresh air is drawn into theinterior of the cigarette through the perforation of the mouthpiecelining paper. The smaller the perforation holes at a constant holedensity or number, respectively, the larger the drag resistance causedthereby; therefore, the smaller the holes, the lower the permeability.Hole density is understood as the hole count per area unit.

In this document diffusivity is understood as being the permeability ofthe mouthpiece lining paper on account of a difference in concentration.Here, the concentration of carbon monoxide during smoking is higher inthe cigarette than in the ambient air. The diffusion of carbon monoxidethus takes place counter to the direction of the influx of fresh air,from the inside to the outside. The level of diffusion, apart from thedifference in concentration, is dependent on the area A which isavailable for diffusion.

Here, many small holes having the same permeability P as a few largeholes in total have a larger area A than the few large holes. Thus,diffusion may be maximized by way of perforating as many holes aspossible which are as small as possible while keeping the permeability Pconstant.

The permeability P of the mouthpiece lining paper may be modified by wayof the perforation parameters of hole size and hole count. Here, thepermeability P may be approximated by using the formula

$P = {\frac{\pi}{8\eta}\frac{{nr}^{4}}{d\; \Delta \; p^{v - 1}}}$

Here, η describes the dynamic viscosity of air. n is the hole count. ris the hole radius. d is the thickness of the paper. Δp is the pressuredifferential between the outer side and the inner side of the paper, andv is an empirically determined permeability exponent which depends onthe perforating method.

The diffusion rate of carbon monoxide from the cigarette is derived inan approximate manner as the product of the coefficient of diffusion ofcarbon monoxide in air and of the area A which is available fordiffusion. For the present observation it suffices to state that thediffusion rate increases the larger the area A which is available fordiffusion. This area A is derived from the area of a hole r²Π multipliedwith the hole count n

A=nr²Π

In the case of a constant permeability P the ratio of the hole count nto the hole radius r is to be selected such that the sum of the holeareas is maximized. The correlation of permeability P, hole radius r,hole count n, and diffusion area A is shown in FIG. 1. In the case of aconstant value of the permeability P, the radius r of the holes steadilydecreases as the hole count n increases. Conversely, the diffusion areaA (=r²Πn) increases as the hole count n increases and the hole radius rdecreases. In order to maximize the diffusion of carbon monoxide throughthe mouthpiece lining paper, it is thus necessary to maximize the holecount or to minimize the hole size, respectively.

The limiting factor in this context is the hole size, since the latter,depending on the perforation method and type of mouthpiece lining paperemployed for technical reasons cannot be implemented so as to be of anarbitrarily small size. However, it is possible to control theperforation parameters such that the achievable minimum hole diameterD_(min) is obtained.

Since this achievable minimum hole diameter D_(min) depends on manyparameters (paper thickness d, coating and type of paper, air humidity,air pressure, deviations in the output of the energy source etc.), it isprovided according to the invention that the hole diameter D is measuredinline by optical means and the measured values are used for regulatingthe perforation parameters (output of the energy source; duration of theenergy pulse; spacing of the energy source from the paper web; type,volume, and pressure of the gas supply; speed of the paper web etc.).

The perforation-hole count is adapted to the achievable minimum holediameter D_(min). This may take place by way of calculation or byoptical measurement of the permeability P of the perforated paper web.

By way of calculation the hole count n results from

$n = {\frac{8\eta}{\pi}\frac{P_{soll}d\; \Delta \; p^{{v - 1}\;}}{r^{4}}}$

The nominal permeability P_(soll) may be indirectly stated by way of thedegree of ventilation or by way of the smoke values of the cigarettemanufacturer, respectively. η, Δp and v are constant, or depend on theperforating process used, respectively. The required hole count n maythus be calculated when the paper thickness d and the hole radius r, orthe hole diameter D (D=2r) are measured, respectively.

Preferably, the permeability P of the perforated paper is measured in anadditional second control loop and the hole count n is correspondinglycontrolled so as to keep the permeability P to the nominal value.

The implementation having two independent control loops is possible ifand when the perforation parameters for regulating the hole size have noinfluence on the hole count n and conversely the hole count n has noinfluence on the hole diameter D.

In many perforating heads the hole count n may be obtained, for example,in that no energy impulse is applied to individual perforating heads. Inthe case of a single perforating head the hole count n may be obtainedin a controlled manner by way of the number or the frequency of theenergy impulses, respectively.

A plasma perforating head for plasma-perforating a paper web, inparticular a mouthpiece lining paper web or a mouthpiece lining paper 4is illustrated in FIG. 2. An energy source which is as small as possiblein terms of area is disposed on at least one planar side of themouthpiece lining paper 4. In this example a needle-shaped electrode 2or more specifically, the brief application of high voltage (AC voltageor DC voltage) between two electrodes 2, 5, is used as an energy source.Perforating may take place in a normal atmosphere, or in a special gasatmosphere, such as a protective gas atmosphere or an atmosphere havinga definable gas composition. Here, the atmosphere may have normalpressure or a pressure which is higher or lower in relation to theenvironmental pressure (air pressure).

Preferably, the gas composition may be modified directly at the locationof the plasma, independently of the environmental atmosphere.

To this end the electrode 2 preferably is attached in a pipe 1. The pipe1 serves for conveying a pressurized gas or gas mixture. For improvedclarity the gas flow in the figures is visualized using arrows. A nozzle1.1 is located at the front end of the pipe 1. This nozzle 1.1 isattached so as to be concentric around the electrode 2, in the region ofthe tip of the latter which faces the mouthpiece lining paper 4. Apressurized gas or gas mixture is thus introduced in an annular manneraround the electrode 2 in the direction of the mouthpiece lining paper 4through the cavity 1.2 which is enclosed by the pipe 1 and the nozzle1.1. A needle-shaped counter electrode 5 which is implemented in alikewise manner, or a planar counter electrode 5 as shown in FIG. 3, maybe located on the other side of the tipping paper 4.

By introducing an inert gas or a gas mixture having a high concentrationof inert gas through the cavity 1.2, a narrow region having another gascomposition remains in the centre of this gas flow, that is to saydirectly in front of the tip of the electrode 2, towards the mouthpiecelining paper 4. The concentration of inert gas in this region issomewhat lower than in the direct flow from the nozzle 1.1. On accountthereof, it is more easily possible for the gas to be ionized in thisregion and to thus produce a localized plasma 3 which by way ofsublimation ultimately produces a hole in the mouthpiece lining paper 4.Since there already is a high concentration of inert gas in and, aboveall, around the plasma 3, oxidation on the surface of the mouthpiecelining paper 4 is precluded, on account of which visible burn marks onthe periphery of the hole are avoided. The expansion of the regionhaving a low concentration of inert gas, and thus of the plasma 3, maybe enlarged or reduced by way of a tight or somewhat wider design of thenozzle 1.1, or by modifying the distance by which the electrode 2protrudes from the nozzle 1.1.

Apart from the frequency, duration, and amplitude of the voltageimpulses between the electrodes 2, 5, preferably at least one of thefollowing parameters is controllable in the regulating method accordingto the invention:

-   -   the opening diameter of the nozzle;    -   the spacing between the nozzle and the electrode tip;    -   the spacing of the electrode from the paper web;    -   the web speed;    -   the gas pressure;    -   the gas composition;    -   the flow volume of the gas.

In the case of the usual arrangement of a multiplicity of needleelectrodes 2, preferably the opening diameter of the nozzle and/or thespacing between the nozzle and the electrode tip may be controlled,since these modifications take place directly at the effective locationof the plasma and thus have a temporally very immediate effect onperforating.

Moreover, these two parameters may be obtained individually on eachelectrode 2, independently of the other electrode 2, on account of whicheach individual electrode 2 can be controlled to the minimum holediameter D_(min) which is achievable therefor.

FIG. 4 shows a preferred perforating head according to the invention,having a laser beam 6 as an energy source. Perforating may take place ina normal atmosphere such as a special gas atmosphere, such as aprotective gas atmosphere or an atmosphere having a definable gascomposition. Here, the atmosphere may have normal pressure or a pressurewhich is higher or lower in relation to the environmental pressure (airpressure).

Preferably, the gas composition may be modified directly at the locationof the plasma, independently of the environmental atmosphere.

To this end, again a nozzle 1.1 is disposed at the lower end of the pipe1. A lens 7 which handles two tasks is located so as to be centric inthis nozzle 1.1. The lens 7 firstly serves for focussing the laser beam6 onto the surface of the mouthpiece lining paper 4. Secondly, the lens7 serves for influencing the gas flow out of the nozzle 1.1 in thedesired manner, specifically in such a manner that the gas flow takesplaces so as to be annular around the lens 7. In order for the inert gasor gas mixture to be able to flow out spherically around the lens 7, thelatter is fixed in the pipe 1 by way of thin wires, for example, or islocated at the end of a rigid optical wave guide which, like theelectrode 2, runs perpendicularly in the pipe 1. In this case, theplasma 3 is limited to that region in which the energy density of thelaser beam 6 is sufficiently high in order for the gas mixture to beionized with a sufficiently low concentration of inert gas. The energydensity of the laser beam 6 is at its maximum in the focal point of thelens 7, and the concentration of inert gas is at its lowest there, suchthat a local, small-area plasma 3 can be produced.

Apart from the output, focal length, frequency, duration and geometry ofthe laser pulses, preferably one of the following parameters iscontrollable in the regulating method according to the invention:

-   -   the opening diameter of the nozzle;    -   the spacing between the nozzle and the lens, or the light guide        tip;    -   the web speed;    -   the gas pressure;    -   the gas composition;    -   the flow volume of the gas.

Nitrogen (N₂), argon (Ar), helium (He), neon (Ne), or carbon dioxide(CO₂) may be employed as an inert gas. It is also possible forindividual types of inert gas to be combined with one another usingspecific mixing ratios or to be combined by flowing through the nozzlesinto the treatment space. Since the inert gas or gas mixture exits thenozzle 1.1 under pressure, the density of the gas or of the gas mixturein the annular region spherically around the electrode 2 or the lens 7is higher than in the region directly in front of the electrode 2 or thelens 7. The denser a gas, the more energy is required for ionizing saidgas. Additionally, ions and electrons are flushed away by the gas flow.These two effects also contribute towards the plasma 3 being localized.

Regulating the hole diameter D may thus also take place in the case ofplasma perforation if and when compressed air is employed as the gasmixture.

FIG. 5 schematically shows the first regulation variant according to theinvention. Here, the hole size, or the hole diameter D and the holeradius r which can be calculated by way thereof, respectively, iscontrolled by way of the innermost of the two illustrated control loops,and the hole count n is controlled by way of the outermost control loop.

The hole radius r, or the hole diameter D, respectively, is measured bythe measuring device 12. The controller 13 controls the control factor uof the actuating element 14, in order to reduce the hole radius r to theachievable minimum hole radius r_(min). The achievable minimum holeradius r_(min) may be determined in an adjustment phase, for example, inthat the hole radius r is reduced by way of a modification of theperforation parameters until the produced plasma is too weak forperforating a hole in the paper at all. The nominal value in the form ofthe achievable minimum hole radius r_(min) is obtained after adjustingto somewhat above the critical hole radius below which perforating is nolonger reliable.

The controller 13 supplies a control factor u which acts on theactuating installation 14. The actuating variable y, such as, forexample, the gas pressure, the gas composition, the nozzle diameter, orthe spacing of the nozzle from the tip of the energy source may bemodified by way of the actuating installation 14. The modification ofthe actuating variable y causes a modification of the plasma 3 on thepaper web 4 (control path 11), which results in a change in the holeradius r.

The measuring device 22 measures the permeability P, preferably by meansof electromagnetic waves as shown in EP 0056223 A2. The number n ofperforation holes is controlled by the difference between the measuredvalue and the pre-defined nominal value P_(soll). The control factor u′has the effect of switching on or switching off individual perforatingheads.

For example, the measuring device 12 may be a linear camera (for examplea high-resolution CMOS or CCD camera of an optical [laser] micrometer)which is directed onto the paper web and takes images of the perforationrows of the paper web in a manner which is synchronized with theperforating devices, such that the number of perforation holes and thehole diameter D thereof of one perforation row are determinable fromanalysing the image in a data processing system.

FIG. 6 shows the control loop of a second variant of the regulationaccording to the invention. Here, in an adjustment phase, the hole sizeis initially reduced by modifying selected perforation parameters up tothe point until, for example, only 50 to 80% of all energy pulses of theenergy source (electrodes 2 or laser beam 6) actually lead toperforation, the ratio of energy impulses which produce a plasma toenergy impulses which do not lead to a plasma discharge in the followingbeing referred to as a “discharge rate”. Thereafter, preferably othercontrol parameters are used for controlling the energy density in such away that the required permeability P_(soll) is derived from theresulting discharge rate.

For example, minimizing the hole size in the adjustment phase may beperformed in that the gas pressure or gas flow rate is increased, or thegas composition is varied, at constant output of the energy source untila discharge rate of 75% is achieved. Thereafter, these gas parametersare kept constant, and the parameters of the energy source (for example,duration, frequency, amplitude of the energy impulse) are controlledsuch that the permeability P assumes the pre-defined nominal value byincreasing or decreasing the discharge rate.

Should it be encountered that the required permeability P_(soll) isnevertheless undershot at the maximum discharge rate, the hole size hasto be somewhat widened at the expense of diffusivity, for example byreducing the gas pressure, reducing the proportion of inert gas in thegas mixture, or adapting the web speed. A measuring device 32 whichmetrologically acquires the hole count n (or the hole density,respectively), the hole size (hole radius r) and the permeability P isprovided for implementing this variant. The data of the measuring deviceis analysed in a data processing system, and one actuating variable (ora plurality thereof) is/are generated by a controller 13 which may beimplemented as software.

Preferably, the data processing system can calculate and store the totalarea of perforation by multiplying the hole count n with the mean holesize, wherein the total area of perforation may represent a key figure(diffusion area A) for the diffusivity of the paper, or the diffusivityof the paper may be calculated therefrom.

In addition to the hole count n (or hole density, respectively), thehole size (hole radius r), and the permeability P, it is advantageousfor the thickness d of the web to be also acquired. Preferably, anon-contacting method for continuously measuring the paper thickness dis employed; such methods are known in the prior art and are shown inthe documents U.S. Pat. No. 4,107,606 (A), EP0995076 (A1), U.S. Pat. No.6,281,679 (B1), for example. The measuring device for measuring thepaper thickness d here may be disposed preferably ahead of theperforating device, or else after the perforating device, when viewed inthe direction of the web.

Particularly in the case of paper varieties having intensely varyingproperties (thickness d and permeability P of the base paper, orthickness d of a coating), it may be necessary to perform measuring ofpermeability, in addition to measuring thickness, ahead of theperforating device. In this case the required number of perforationholes for the perforation which follows in each case may beapproximately calculated from the paper parameters and the achievableminimum hole diameter D and may optionally be controlled in that theformula is adapted by way of the measured values of a measuring device,which is disposed after the perforating device, for measuring theactually achieved permeability P. Alternatively, the discharge rate mayalso be controlled, depending on the thickness d and the permeability Pof the base paper.

In FIG. 7 an exemplary plasma perforating device according to theinvention is shown, having a rail with eight perforating heads and ameasuring device 8. The number of eight perforating heads here resultsfrom reasons of clarity; in the case of a practical implementation thenumber of perforating heads may be for example between 15 and 30 perrail, wherein a plurality of rails may be disposed so as to be parallelwith one another—either behind one another and/or beside one another.The paper web 4 is continuously moved from left to right through thedevice, optionally at a variable speed. It is also possible for two ormore paper webs to be perforated which bear on one another and thus formmultiple layers to be simultaneously guided through the perforatingdevice.

Particularly preferably, the measuring devices 12, 22 are configured asone measuring device 8, the signal of which is analysed in a dataprocessing system 9. The data processing system 9 determines the radiusr, the hole count n, and the permeability P, and by way of controllers13, 23 which are implemented as software generates the control factorsu, u′. Preferably, the hole radius r or the hole diameter D,respectively, is acquired for each perforating head, in order forparameters to be able to be modified in a targeted manner on individualperforating heads, or in order to be able to react in the event thatindividual perforating heads produce significantly larger perforationholes than others, for example on account of wear.

Instead of the nominal permeability P_(soll) (in CORESTA units CU), thedegree of ventilation, drag resistance and/or the smoke values to beachieved may also be entered into the data processing system. Thenominal permeability P_(soll) may in turn be calculated by way of acalculation rule which is stored in the data processing system.

The hole radius r or the hole diameter D, respectively, the hole count nor the hole density, respectively, and the permeability P serve as inputvalues for the data processing system. The paper thickness d, thepermeability P of the base paper, the type and thickness of an optionalcoating, and the web speed are additional input values. If and when thethickness d and the permeability P of the base paper, or the coating,respectively, are constant across the entire paper web, it is sufficientfor these values to be input into the data processing system prior tothe commencement of perforating. Above all, if and when the permeabilityP of the base paper or of the coated paper are negligibly minor incomparison to the permeability P achieved by perforating, theconsideration of the permeability P of the base paper may be dispensedwith. The hole radius r and the hole count n are metrologically acquiredby the measuring device 8 after the perforating device, whereinpreferably the permeability P is also acquired by the measuring device8, or, using the hole count n, the hole radius r, and the thickness d ofthe paper web, the data processing system can calculate the permeabilityP according to this formula (or other formulae):

$P = {\frac{\pi}{8\eta}\frac{{nr}^{4}}{d\; \Delta \; p^{v - 1}}}$

The web speed serves as an input value of the data processing system andmay also serve as an output value (actuating variable) in the event ofthe web speed having to be controlled depending on the input values.Further output values (actuating variables) may include: the frequency,duration, and amplitude of the voltage impulses between the electrodes2, 5; the spacing of the electrode from the paper web; the spacing ofthe nozzle from the electrode tip; the output, focal length, frequency,duration, and geometry of the laser impulse; the spacing between thenozzle and the lens or the tip of the light guide; the gas pressure; theopening diameter of the nozzle; the gas composition; the flow rate ofthe gas.

In contrast to the prior art the present invention is advantageous sincethe influence of the perforation on the reduction of carbon monoxide bydiffusion is considered, so that for the first time adiffusion-optimized perforation of mouthpiece lining paper is carriedout and thus for the first time a diffusion-optimized perforatedmouthpiece lining paper is manufactured.

Moreover the method for plasma perforating is particularly advantageousin this context, since besides the classic controllable parameters of aperforating device (output, duration, frequency of the energy impulsesof the energy source, and web speed), by way of the targetedintroduction of gas or gas mixtures further controllable parameters (gaspressure, gas amount, gas composition, nozzle geometry) which enabletargeted reduction of the hole size are available, and higher holedensity may also be achieved by way of the enhanced positioning accuracyof the holes which is additionally enabled by plasma perforation.

1. A method for manufacturing a diffusion-optimized mouthpiece liningpaper for tobacco products, in particular filter cigarettes, byperforating the web of the mouthpiece lining paper for the purpose ofmaximum reduction of carbon monoxide, wherein the diffusivity and thepermeability P of the perforated mouthpiece lining paper are determinedinline, and the diffusivity is maximized by regulating the perforationparameters while constantly adhering to the pre-definable nominalpermeability P_(soll).
 2. The method according to claim 1, wherein thenominal permeability P_(soll) is pre-defined by pre-defining the degreeof ventilation, the drag resistance and/or the smoke values to beachieved.
 3. The method according to claim 1, wherein diffusivity isapproximately determined in that the perforation-hole count, or thedensity of holes and/or the hole diameter D, respectively, aremetrologically acquired.
 4. The method according to claim 1, wherein thepaper thickness d is measured inline.
 5. The method according to claim1, wherein the perforation parameters are controlled such that theachievable minimum hole diameter D_(min) is set and permeability P isheld constant by regulating the hole count n.
 6. The method according toclaim 5, wherein the achievable minimum hole diameter D_(min) for themouthpiece lining paper being used is determined in an adjustment phaseby automatic or manual variation of the perforation parameters.
 7. Themethod according to claim 1, wherein the hole diameter D ismetrologically acquired, and the required hole count n is determined bycalculation, preferably by way of the formula
 8. The method according toclaim 1, wherein the hole size is minimized in that the energy densityof the plasma is reduced so far that preferably only approx. 50% to 80%of the energy impulses of the at least one energy source lead toperforation and the perforation parameters subsequently are controlledsuch that, on account of the change in the energy density of the plasma,the perforation-hole count or the hole density, respectively, isobtained at which the actual value of permeability P is equal to thenominal permeability P_(soll).
 9. The method according to claim 8,wherein regulating the hole size is established by one or a plurality ofthe following measures: modifying the gas pressure; modifying the gasflow rate; modifying the gas composition, in particular modifying theconcentration of inert gas; modifying the opening area of the nozzle;modifying the distance by which the tip of the energy source projectsfrom the nozzle; modifying the web speed.
 10. The method according toclaim 8, wherein regulating the number of energy impulses of the atleast one energy source which lead of a perforation is performed in thatthe frequency, duration and/or amplitude of the voltage impulse on theelectrodes are/is modified, or in that the output, focal length,frequency, duration and/or geometry of the light impulses of one or aplurality of laser beams are/is modified.
 11. The method according toclaim 1, wherein perforating is simultaneously performed by a pluralityof perforating heads, wherein the hole diameter D of each produced holeis determined, wherein in the data processing system each perforationhead is assigned the diameter of the hole produced therewith.
 12. Adevice for perforating a web of mouthpiece lining paper, wherein atleast one energy source is directed at an angle of preferably 90° ontothe mouthpiece lining paper, and wherein this energy source includes atip from which an energy beam is directed onto the mouthpiece liningpaper, wherein when viewed in the web direction a measuring device whichacquires the size and the number or density of the perforation holes,respectively, and the permeability P of the mouthpiece lining paper isdisposed after the perforating device, a data processing system, by wayof which the data of the measuring device is convertible to at least onecontrol factor for regulating the perforation parameters, is provided.13. The device according to claim 12, wherein the mouthpiece liningpaper in the perforating device is surrounded by a gas atmosphere whichin relation to the ambient atmosphere has a higher or lower proportionof inert gas and/or a lower or higher pressure.
 14. The device accordingto claim 13, wherein each energy source is attached in a pipe on the endof which that faces the mouthpiece lining paper a nozzle which serves asan exit opening for a pressurized gas or gas mixture is disposed,wherein the tip of the energy source is disposed in the nozzle so as tobe concentric.
 15. The device according to claim 12, wherein each energysource is formed by an electrode, wherein at least one counter electrodeis provided on the other side of the mouthpiece lining paper.
 16. Thedevice according to claim 15, wherein a high voltage in the form of DCor AC voltage is applicable between the electrodes.
 17. The deviceaccording to claim 12, wherein the energy source is a laser.
 18. Thedevice according to claim 12, wherein a device for measuring thethickness d of the web of the mouthpiece lining paper inline isprovided.